Unexpected structural preference with metallophilic Ag–Au contacts in silver(i)-N-heterocyclic carbene cluster; experimental and theoretical approach

Abstract

A novel synthetic donor-atom-selective approach has been adopted for the synthesis of a heterobimetallic cluster of a new NCN-pincer, 1,3-bis-(1-methyl-1H-benzo[d]imidazol-2-yl-methyl)-1H-imidazol-3-ium hexafluorophosphate (1·HPF₆). The complex [Ag₃(1)₃][PF₆]₃ (2) has been prepared via the Ag₂O route; which undergoes transmetallation to yield a cluster that seems to be the first example of the heterobimetallic trinuclear system [Au–Ag₂(1)₂Cl][PF₆]₂, 3. Finally, the trinuclear cluster geometries of 2 and 3 were confirmed via SCXRD studies. Interestingly, Au(I) binds preferentially with soft donor C_carbene, which transmetallated from the cluster of 2. In both the cyclic trinuclear clusters, the M–M interactions were further inspected using gauge independent atomic orbital (GIAO) computations. Both 2 and 3 are luminescent and possess σ-aromaticity; the NICS values indicate that 3 is more aromatic than 2.